The controversy which dogged Lance Armstrong throughout this year's Tour de France will begin its end-game today in the central Italian town of Bologna, when the Texan's trainer and confidant Dr Michele Ferrari enters its court-house to answer four separate charges of supplying banned drugs to elite cyclists over a lengthy period in the 1990s.

Armstrong is not on the long list of cyclists alleged to have been supplied by Ferrari but, en route to his third successive win in the Tour this summer, cycling's biggest star repeatedly and loudly declared his belief in his trainer's probity. If Ferrari is found not guilty, Armstrong's stand will be vindicated. On the other hand, if the charges stand, it will be a grave embarrassment for the American, who has said that in that event he would consider dispensing with the Italian's services.

The slight, studious-looking Dr Ferrari denies that he provided erythropoietin (EPO), human growth hormone, adrenalin, Insulin Growth Factor, Dhea, testosterone and corticosteroids to a number of cyclists "in a manner prejudicial to health", as the charge sheet puts it. His fellow accused, Massimo Guandalini, proprietor of a pharmacy called Giardini Margherita, admitted the charges on a plea-bargain basis at an initial hearing in February.

The evidence drawn up by the investigating magistrate Giovanni Spinosa includes tapped telephone calls, prescriptions apparently signed by Ferrari, a list of drugs found in Ferrari's house during police searches, and cyclists' training programmes. Ferrari is also accused of illegally importing folic acid-based substances, which can be used in conjunction with EPO to boost the red-cell count in an athlete's blood.

The doctor is confident that he will be found not guilty. "None of the interrogated riders have told the police that I have given them illegal medicines. I don't think I will be convicted. But naturally it isn't pleasant to think about the risk."

Just before this year's Tour Armstrong confirmed rumours which had circulated in the cycling world for six years that he worked with Ferrari and during the race he was questioned about their relationship in a long, tense press conference on the race's rest day in the Pyrenees. Armstrong's position is that the doctor is innocent until proven guilty and that he personally has never been given grounds to suspect him of any wrongdoing.

Asked why he had not stopped working with Ferrari when it was known that he was facing charges, he said: "I'm confident in the relationship, I've never denied the relationship. I believe he's an honest man, I believe he's an innocent man. I've never seen something to make me believe otherwise."

The doctor, in his only interview in the last seven years, revealed that the pair have had a close working relationship over the past five years, since the Texan began his comeback from testicular cancer. Speaking recently to the Danish newspaper Ekstra Bladet, Ferrari said that, when Armstrong is racing, he is in daily contact with the rider by telephone.

This is not surprising, as that is how Ferrari worked with other cyclists. But Ferrari painted a new picture of the way they work by revealing that Armstrong had even called him for advice during a mountain stage of the Tour de France, using a mobile phone belonging to Armstrong's team manager Johan Bruyneel, who follows the race in the team's car.

"During the Tour de France in 2000 Lance called me in the course of the stage that finished in Courchevel, where Marco Pantani attacked before withdrawing from the race the next day. Pantani's attack was a good distance from the finish and I advised Lance to take it easy and let him go."

Ferrari added that he spoke to Armstrong on two or three occasions during the 2000 Tour in this way. For any coach in cycling to make such an intervention is virtually unheard of and implies an extremely close relationship.

Armstrong is not the only major name in cycling who faces embarrassment if Ferrari is found guilty. In the mid-1990s many of the world's top cyclists made their way to his office in the city of Ferrara. The list of the doctor's clients is topped by the triple Tour of Spain winner and Tour de France runner-up Tony Rominger, who was the world No1 between 1994 and 1996.

Also named are a host of major figures from the 1990s, including Claudio Chiappucci, the runner-up in the 1990 and 1992 Tours de France, Spain's 1995 world champion Abraham Olano, Mario Cipollini, the flamboyant sprinter who won four stages in a row during the 1999 Tour, and Axel Merckx, the son of cycling's non-pareil Eddy. Armstrong's former close friend Kevin Livingston is also on the list. They have all been cited as injured parties by Spinosa and will therefore not face charges and are unlikely to appear as witnesses.

Since the Tour de France drugs scandal of 1998, cycling has been on trial in a number of high-profile court cases: the Festina trial in 1998, Marco Pantani's indictment last year and this year's trials involving the supply of narcotics and EPO. Today is different, however: Ferrari's extensive list of clients means that the credibility of almost a decade of results could be undermined if he is found guilty.